Re: Branches and transformer model

[Jean-Francois Simon]

Thanks Russ

Jean-François


Le 09/08/2021 à 17:18, Russ Patterson a écrit :

Hi Jean- François,

I think the transformer impedance should be converted to and specified on the base MVA used in the study (mpc.baseMVA).

Best regards,

russ

*From:*bounce-125822131-88411...@list.cornell.edu [mailto:bounce-125822131-88411...@list.cornell.edu] *On Behalf Of *Jean-Francois Simon

*Sent:* Monday, August 9, 2021 10:52 AM
*To:* MATPOWER discussion forum
*Subject:* Re: Branches and transformer model

Hi Ray,

Thank you,

I found out there must be 1 at the tap to make Matpower understand the branch as transformer,

this is ok, and the impedance in per unit, 14% is 0.14.

For example branches:

  1 2   0.001 0 0     250 250 250 0 0 1 -360 360; Is a power cable

  2 3   0.001 .105 0  250 250 250 1 0 1 -360 360; Is a transformer impedence 10.5%   2 4   0.001 .12 0   250 250 250 1 0 1 -360 360; Is a transformer impedence 12%

What I don't understand, as you stated, is where do we specify the transformer MVA rating, which

should take part in the calculation except my misunderstanding.

For instance both are 16 MVA transformers.

So I just set the above values and made a calculation without indicating the transformer apparent

power, as I could not find if it matters and where to specify.

Regards,

Jean-François

Le 09/08/2021 à 16:42, Ray Daniel Zimmerman a écrit :

Yes, in the current MATPOWER case format v2, the transformers are specified in 
the same branch matrix as the AC transmission lines. I’m a bit rusty on my 
transformer modeling, so someone please correct me if I’m wrong, but I believe 
the % impedance specification is equivalent to the p.u. impedance value 
expressed using the transformer rated power and voltages as the per-unit bases. 
So I think you just have to convert the impedance to the system per-unit bases 
to put it in the branch matrix.
    Ray

    On Aug 2, 2021, at 9:49 AM, Jean-Francois Simon<jfsi...@startmail.com>  
<mailto:jfsi...@startmail.com>  wrote:

    Good day,

    I am learning MatPower and have a case to study with 8 buses. The below 
example a simplification:

    I could understand how to build buses and links and simulate the energy 
flow. Results look right,

    however I have a question since the buses are working on different voltage 
levels, hence some

    links have power transformers.

    *** Bus 2: 90 kV - Feeder bus ***

    *** Bus 3: 30 kV - Load bus ***

    *** Bus 5: 690 V - Load bus ***

    <Bus 2>---(90/30kV XFR)---<Bus 3>---(30/.69 kV XFR)---<Bus 5>

    Bus 2 to bus 3 is a 16 MVA transformer with impedance 10.5%

    Bus 3 to bus 5 is a 5 MVA transformer with impedance 6.5%

    At the moment, the bus definition looks like this:

    mpc.bus = [

    2    3    0.0    0.0    0    0    1        1    0    90.0 1    1.1    0.9;

    3    1    7.2    2.1    0    0    1        1    0    30.0 1    1.1    0.9;

    5    1    3.5    0.1    0    0    1        1    0    0.69 1    1.1    0.9;

    ];

    And branches definition is incomplete:

    mpc.branch = [

       2 3   0.1 0 0   250 250 250   0 0 1 -360 360;

       3 5   0.1 0 0   250 250 250   0 0 1 -360 360;

    ];

    Is this right transformers are set in "Branches" ? How do we calculate and 
set resistance branches

    resistance and and reactance in order to properly integrate transformers as 
for example in above

    case ?

    Thank you for support,

    Regards,

    Jean-François Simon